How does radiation make us feel warm?

  • 1 Replies

0 Members and 1 Guest are viewing this topic.



  • Guest
How does radiation make us feel warm?
« on: 03/10/2008 22:03:59 »
Tom asked the Naked Scientists:

A theory crossed my mind about frequency.  Since frequencies from the sun, radio, etc., up to infrared, are too low in voltage and frequency, the frequency makes its' way beyond most of the "sense of touch" nerves, deeper into the body, therefore no sensations are felt. Beyond inferred, the frequencies are so high that to the nervous system, the positive and negative of each wave virtually cancel out each other before they penetrate the skin, and create a sensation (except for microwaves). But at inferred light frequencies, the frequency is at just the right level that there is slight feedback from each positive and negative section of each wave, causing conduction in the skin, just like a wire/inductor (possibly due to the 90 degree phase shift between voltage and current, and/or the impeadence level, and/or the the 5 time constants that it takes for the voltage to reach peak (in other words - delay)) therefore, making the one charge inside to act like a small battery, when the opposite polarity comes in, creating a small amount of wattage/heat in the skin, and over time causing a person to feel warm. Could this be true?

Tom Sexton

PS I'm 40 years old...

What do you think?



  • Guest
How does radiation make us feel warm?
« Reply #1 on: 03/10/2008 23:30:19 »
As far as I am aware, there are no nerves which respond to em waves in a coherent way (i.e. like a radio receiver).
The sensors in the eye are activated by the photons (in the visible region) and produce electrical impulses from an electrochemical process. I don't know of any nerves which are stimulated by electrical signals higher than audio frequencies.
However, all frequencies of radiation are absorbed to a greater or lesser extent, by body tissue.
Electrical currents can be induced in your body in the same way as in a radio antenna.  If the wavelength is of the order of your body size you will get a slight resonance. so you might expect this to happen for frequencies in the VHF region but to calculate the current for lower frequencies the induced current  just a matter of volts per metre times your height divided by a resistance value equivalent to salty water. (P = Vsquared/ R)
There will be a rise in body temperature if the field strength is high enough - but you'd need to be standing right next to a broadcast antenna to 'feel' anything. The RF content from the Sun is very low.
At microwave frequencies, there are absorption bands where the water and fat molecules extract the power much better. (As in ovens).
With for very short wavelength microwaves, infra red and light, the molecules near the surface just absorb the energy before it penetrates very far.
But, in all these cases, the effect is essentially, a thermal one; electrons are forced to vibrate about their rest position by the RF field and dissipate energy.  The absorbed energy is transferred to heat.

Re your comment about the phase shift. Any power dissipated is due to the in-phase /real components of V and I. (VI Cos(phase)). Any out of phase component is just reactive power and would pass through or be reflected. It is hard to discuss this aspect for something as vague as a body and you really need to look at some basic antenna theory and approach the question from that direction. i.e. a simple model to start with.